<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>双飞翼布局</title>
</head>
<body>
<header></header>
<section>
    <div class="main">
        我是主列，出来吧！
    </div>
    <div class="sub">
        我是子列
    </div>
    <div class="extra">
        我是附加列
    </div>
</section>
<footer></footer>
</body>
<style>
    * {
        padding: 0;
        margin: 0;
    }

    header, footer {
        background-color: red;
        min-height: 200px;
    }

    .sub, .extra {
        width: 200px;
        min-height: 200px;
        float: left;
    }

    .extra {
        width: 200px;
        min-height: 200px;
        float: left;
    }

    .main {
        float: left;
        width: 100%;
        min-height: 200px;
        margin-left: 200px;
        margin-right: 200px;
        background-color: #5e001f;
    }

    .sub {
        margin-left: -100%;
        background-color: #333;
    }

    .extra {
        margin-left: -200px;
        background-color: blue;
    }

    footer {
        clear: both;
    }
</style>
</html>